Friction welding sintered materials

ABSTRACT

Friction welding porous sintered materials, such as sintered steel, sintered copper and sintered alloys thereof to each other and to other metals including process parameters for the welding of these materials.

United States Patent Marion R. Calton East Peoria;

Carl D. Weiss, Peoria, lll. 747,779

July 19, 1968 Mar. 23, 1971 Caterpillar Tractor Co. Peoria, Ill.

lnventors Appl. No. Filed Patented Assignee FRICTION WELDING SINTEREDMATERIALS 4 Claims, 3 Drawing Figs.

U.S. Cl 29/4703,

[5 1] Int. Cl B23k 27/00 [50] Field of Search 29/4703; 228/2; 156/73Primary Examiner-John F. Campbell Assistant Examiner-Robert J. CraigAttorneyFryer, Tjensvold, Feix, Phillips & Lempio ABSTRACT: Frictionwelding porous sintered materials, such as sintered steel, sinteredcopper and sintered alloys thereof to each other and to other metalsincluding process parameters for the welding of these materials.

PATENTED W23 I971 SHEET 1 UF' 2 MARION RCALTON CARL D. WEISSPATENTEDmzsmn a; 571,905

SHEET 2 OF 2 SINTERED SAE I080 STEEL &- i -sAE I040 STEEL INVENTORSMARION R. CALTON CARL D. WEISS W A TORNEXS FRTQTTON WELEENG SENTEREDMATERIALS BACKGROUND OF THE INVENTION This invention relates toimprovements in friction welding of the general type wherein twoworkpieces are subjected to relative rotation while in rubbing contactwith each other to generate frictional heat to raise the workpieces to asuitable welding temperature, whereupon the relative rotation subsidesand a bond is formed between the workpieces.

The invention is particularly directed to the joining of porous sinteredmaterials to each other and to other materials by the friction weldingprocess. The invention is more specifically directed to the frictionwelding of various compositions of sintered steel and sintered copper,and includes the welding parameters which are used to produce good weldswith these compositions.

It is also to be understood that the invention is applicable to theinertia friction welding process as described in US. Pat. No. 3,273,233and as set forth below.

In the inertia welding process the energy required to bring the commoninterface of the parts to a bondable condition is stored as kineticenergy in rotating inertia weights. These weights generally take theform of flywheels and are connected to one of the parts and the entireenergy necessary to form the bond is stored in the weights prior to theengagement of the parts at the interface. The stored energy isdischarged into the interface through frictional heating and plasticworking developed at the interface as the rubbing contact slows therotating weights and the bonding cycle is concluded.

This invention is principally directed toward powder metallurgymaterials which may be classified in the as sintered" or as sintered andheat treated" condition, and containing considerable porosity. Thisclass of materials, which principally includes sintered iron, steel andcopper insofar as most commercial applications are concerned, isconsidered extremely difficult, if not impossible, to weld byconventional welding methods. in fact, these sintered materials aregenerally considered not weldable because of their porosity, andconsequently very little information is available with regard toattempts at conventional welding of porous sintered materials.

The problem involved in conventional welding of these sintered materialsresults from gas and moisture entrapped in the pores of the material.This entrapped gas and moisture makes it very difficult to get anacceptable weld by conventional welding methods and attempts thereatinvariably result in 4 quality welds due to cracking and gas pockets. Ifconventional welding of these porous sintered materials is to be at allsuccessful, a thorough heating and degreasing operation to eliminate theoil or water and gas entrapped in the pores of the material would appearto be a necessary preliminary operation prior to the actual welding ofthe materials. Even with a thorough degreasing and dehydration operationprior to welding, it is very doubtful whether conventional fusionwelding would produce an acceptable bond because of the porosity of thesintered material.

Accordingly, it is the principal object of the present invention tofriction weld the aforementioned sintered materials wherein theinterface of the weld zone is compacted to eliminate voids and a highdensity, hot worked metallic structure is produced which issubstantially nonporous rather than a technically sintered composition.

it is a further object of the invention to provide parameters for thefriction welding of these sintered materials, which parameters result inthe compacting of the material to eliminate voids at the weld zone andproduce a bond comprised of a high density, hot worked metallicstructure.

Other objects and advantages of the present invention will be apparentfrom the following description and claims and are illustrated in theaccompanying drawings which, by way of illustration, show preferredembodiments of the present invention and the principles thereof and whatis now considered to be the best mode contemplated for applying theseprinciples. it is recognized that other embodiments of the inventionembodying the same or equivalent principles may be used, and structuralchanges may be made as desired by those skilled in the art withoutdeparting from the present invention and the purview of the appendedclaims.

BRIEF DESCRlPTlON OF THE DRAWINGS FIG. l is a side elevationillustrating one embodiment of a friction welding machine which may beused to practice the method of the present invention;

FIG. 2 is a photomicrograph illustrating the microstructure of aspecimen of sintered SAE 1,080 steel; and,

FIG. 3 is a photomicrograph illustrating a specimen of sintered SAE1,080 steel which has been bonded to a specimen of SAE 1,040 steel bythe friction welding method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A friction welding machineconstructed in accordance with one exemplary embodiment of the presentinvention is indicated generally by the reference numeral ll in FIG. 1.As shown, the machine comprises a frame or housing structure generallydenoted at 12 for housing the various elements of the machine. The twoparts to be welded, workpieces WP-l and NP-2, are mounted within chucksl4 and 16.

The chuck 16 does not rotate and is mounted on a tailstock fixture 18.The fixture i8 is mountedrfor axial movement on the machine frame 12under the control of a load cylinder 20. A pressure control circuit, notshown, regulates the pressure in the load cylinder, and thus determinesthe force with which the parts WP-l and WP-2 are engaged.

The chuck M is mounted on a spindle 22, and the chuck and spindle aremounted for rotation within the frame 12. The rotary spindle 22 isadapted to receive flywheels 24 which may be of various size and massdepending upon the particular application of the machine.

An electric motor 26 rotates the spindle through a hydrostatictransmission generally indicated by the reference numeral 28. Thehydrostatic transmission includes a hydraulic pump 30, a hydraulic motor32 and a manifold 34 between the pump and motor.

The drive ratio between the motor and the spindle 22 can be varied bychanging the cam angles in either the pump 30 or the motor 32, and thepump and motor can be used to effectively disconnect the motor 26 fromthe spindle 22 by moving the cam and the pump 30 to a position in whichthe pump 30 does not displace any hydraulic fluid to the motor 32.

it is to be understood that the flywheel weights 24 are mounted on thespindle 22 so that the welding machine it can be operated as an inertiawelding machine as described in US. Pat. No. 3,273,233 and as describedin further detail below.

A welding operation to join a first workpiece, such as sintered steel orsintered copper, to a second workpiece such as another porous sinteredmaterial or any other metal such as steel, for example, can be performedby operating the machine in the following general manner. One of theweld pieces WP-l is firmly clamped in the rotatable chuck 14 located onthe spindle 22. The other weld piece WP-2 is firmly clamped in thenonrotatable chuck 16 which is located on the tailstock portion 18 ofthe machine. Upon actuation of the motor 26, the flywheeland workpieceWP! are accelerated to a predetermined velocity.

Once the predetermined velocity has been obtained, the motor 26 isdisconnected or shutdown and the ram mechanism 20 is actuated to movetailstock portion 18 and workpiece WP-Z into contact with the rapidlyrotating workpiece NP-l. As the two workpieces are brought into contactunder the upsetting pressure applied through ram 20, heat is generatedat the contacting surface or interface of the weld flashing, therotational velocity of the spindle member 22 has continued to decrease.At the time the rotation of the spindle ceases, upsetting has takenplace and the weld is completed.

To illustrate the manner in which the friction welding process, andparticularly the inertia friction welding process, has been utilized tojoin porous sintered materials both to themselves and to other metals anexemplary weld will now be discussed with respect to the remaining FIGS.It is to be understood, however, that the following exemplary weld isfor the purpose of illustration and the invention is not to be regardedas limited to any of the specific materials recited with respectthereto.

FIG. 2 is a photomicrograph illustrating the microstructure of anunwelded specimen of a base metal comprised of sintered SAE 1,080 steelmaterial. The specimen illustrated in FIG. 2 has been magnified 500times and etched with a l percent solution of nital (99 percent alcoholand 1 percent concentrated nitric acid). It should be observed that thespecimen of sintered material illustrated in FIG. 2 is quite poroushaving a large percentage of voids indicated by the dark spots andlines. The amount of porosity in this material has been estimated to be30 percent.

FIG. 3 is a photomicrograph illustrating a friction weld by the processof the present invention between the porous sintered SAE 1,080 steel ofFIG. 2 and a workpiece of SAE 1,040 steel. The photomicrograph of FIG. 3has also been magnified 500 times and etched with a 1 percent solutionof nital. The sintered material SAE 1,080 steel material is at the topof the photomicrograph and the SAE 1,040 steel is on the bottom with theweld zone approximately in the center as indicated.

Again it may be observed that the sintered SAE 1,080 steel materialshown at the top of the photomicrograph has a large number of voidsindicated by the dark spots and lines. It should be noted that thesevoids decrease in number as the weld zone is approached and that thevoids completely disappear at the weld line. Because of the high densityat the weld line the weld is at least as strong and probably strongerthan the base material (sintered SAE 1,080 steel).

By utilizing the proper friction welding parameters for the welding ofthese porous sintered materials as the workpieces are relatively rotatedand brought into engagement, a high heat condition is created at theinterface of the workpieces which drives off gas and vapors contained inthe porous sintered material. Thus, any oil or water which is containedin the pores of the sintered material is literally squeezed out of theinterface zone so that at the interface a compacted, high density, hotworked metallic structure is developed rather than a technicallysintered composition.

From the work done involving various samples and test programs,parameter ranges have been established for the friction welding ofporous sintered materials to each other and to other metals. Theseparameter ranges are:

Surface Velocity 500 4,000 feet per minute.

Axial Load or Pressure 5,000-30,000 pounds per square inch.

Input energy l5,00050,000 foot-pounds per square inch.

For sintered steel materials the parameter ranges for producing goodfriction welds are:

Surface Velocity 500-- l ,500 feet per minute. Axial Load or Pressure15,00030,000 pounds per square inch. Input Energy 20,00050,000foot-pounds per square inch. For sintered copper materials the parameterranges for producing good friction welds are:

Surface Velocity 1,8004,000 feet per minute.

Axial Load or Pressure 5,000-30,000 pounds per square inch.

Input Energy 15,000-50,000 foot-pounds per square inch.

The parameters set forth above are the values which are considerednecessary to produce acceptable or good welds when friction weldingthese materials. Acceptab1e" in this sense means complete bonding of theentire interface such that the weld zone is formed into a compacted,high density, hot worked structure which is free of voids andsubstantially nonporous.

Sintered materials which may be friction welded according to the presentinvention include sintered SAE 1,080 steel material, sintered SAE 4,340steel material, sintered SAE 1024 steel material, sintered copper andcopper alloys (such as sintered materials having a copper-tin base oriron-copper base) and many other well known sintered materials.

In addition, friction welds have been made with porous sinteredmaterials of various compositions which were saturated with coolingfluid. These welds were quite satisfactory when performed under theparameter conditions set out above and did not require any thoroughdegreasing operation or similar preliminary procedures to eliminate theoil or water entrapped in the pores of the material since under theprocess of the present invention such oil and water is driven off duringthe welding operation.

While we have illustrated and described preferred embodiments of ourinvention, it is to be understood that these are capable of variationand modification, and we therefore do not wish to be limited to theprecise details set forth, but desire to avail ourselves of such changesand alterations as fall within the purview of the following claims.

We claim:

1. A method of friction welding porous sintered workpieces to each otheror to other metals comprising the steps of effecting relative rotationof the workpieces at speeds of from approximately 500 to 4,000 surfacefeet per minute, forcing the workpieces into frictional engagement attheir common interface under a predetermined axially applied pressure offrom approximately 5,000 to 30,000 pounds per square inch; effecting anenergy transfer at the interface in a range of from approximately 15,000to 50,000 foot-pounds per square inch, which concentrates heat at theinterface until a bond is formed and all the input energy is expended;and wherein the weld zone bond is formed into a compacted high density,hot worked metallic structure which is free of voids and substantiallynonporous.

2. A method of friction welding porous sintered steel workpieces to eachother or to other metals comprising the steps of effecting relativerotation of the workpieces at speeds of from approximately 500 to 1,500surface feed per minute, forcing the workpieces into frictionalengagement at their common interface under a predetermined axiallyapplied pressure of from approximately 15,000 to 30,000 pounds persquare inch; effecting an energy transfer at the interface in a range offrom approximately 20,000 to 50,000 foot-pounds per square inch, whichconcentrates heat at the interface until a bond is formed and all theinput energy is expended; and wherein the weld zone bond is formed intoa compacted, high density, hot worked metallic structure which is freeof voids and substantially nonporous.

3. A method of friction welding porous sintered copper workpieces toeach other or to other metals comprising the steps of effecting relativerotation of the workpieces at speeds of from approximately 1,800 to4,000 surface feet per minute, forcing the workpieces into frictionalengagement at their common interface under a predetermined axiallyapplied pressure of from approximately 5,000 to 30,000 pounds per squareinch; and effecting an energy transfer at the interface in a range offrom approximately 15,000 to 50,000 footpounds per square inch, whichconcentrates heat at the interface until a bond is formed and all theinput energy is expended; and wherein the weld zone bond is formed intoa compacted, high density, hot worked metallic structure which is freeof voids and substantially nonporous.

4. A method as set forth in any one of claim 1, 2 and 3 wherein saidworkpieces are friction welded to each other by the inertia frictionwelding process and wherein one of said workpieces is operatively ass)ciated with a rotating mass, which mass stores the requisite amount ofinput energy to be released at the weld interface.

2. A method of friction welding porous sintered steel workpieces to eachother or to other metals comprising the steps of effecting relativerotation of the workpieces at speeds of from approximately 500 to 1,500surface feed per minute, forcing the workpieces into frictionalengagement at their common interface under a predetermined axiallyapplied pressure of from approximately 15,000 to 30,000 pounds persquare inch; effecting an energy transfer at the interface in a range offrom approximately 20,000 to 50,000 foot-pounds per square inch, whichconcentrates heat at the interface until a bond is formed and all theinput energy is expended; and Wherein the weld zone bond is formed intoa compacted, high density, hot worked metallic structure which is freeof voids and substantially nonporous.
 3. A method of friction weldingporous sintered copper workpieces to each other or to other metalscomprising the steps of effecting relative rotation of the workpieces atspeeds of from approximately 1,800 to 4,000 surface feet per minute,forcing the workpieces into frictional engagement at their commoninterface under a predetermined axially applied pressure of fromapproximately 5,000 to 30,000 pounds per square inch; and effecting anenergy transfer at the interface in a range of from approximately 15,000to 50,000 foot-pounds per square inch, which concentrates heat at theinterface until a bond is formed and all the input energy is expended;and wherein the weld zone bond is formed into a compacted, high density,hot worked metallic structure which is free of voids and substantiallynonporous.
 4. A method as set forth in any one of claim 1, 2 and 3wherein said workpieces are friction welded to each other by the inertiafriction welding process and wherein one of said workpieces isoperatively associated with a rotating mass, which mass stores therequisite amount of input energy to be released at the weld interface.